Aim: This study examined the effect of five months of interval walking training (IWT) on knee extensor and flexor muscle strength and blood pressure in older people based on monthly changes over time.

Methods: Forty-eight elderly subjects (14 men, 34 women; mean age, 70±5 years old) practiced IWT for 5 months. The peak oxygen intake (VO₂peak) was measured before and after the intervention, and knee extension, flexion muscle strength, and blood pressure were measured monthly from the start of the intervention.

Results: A significant increase in the VO₂peak (pre: 20.0±3.2 ml/min/kg, post: 21.3±3.9 ml/min/kg) was observed after 5 months of IWT, along with significant increases in knee extensor (pre: 20.6±6.4 kgf, post: 27.2±9.3 kgf) and flexor (pre: 12.7±4.5 kgf, post: 14.7±5.2 kgf) muscle strength, with knee extensor strength increasing significantly until the third month and knee flexor strength until the second month, after which these values plateaued. Regarding resting blood pressure, a significant decrease in systolic blood pressure was observed after the second month of intervention and a significant decrease in diastolic blood pressure was observed after the fifth month of intervention.

Conclusions: Five months of IWT resulted in an increase in physical fitness due to an increase in the VO₂peak, an increase in lower limb muscle strength, and an improvement in resting blood pressure. However, significant increases in knee extensor and flexor muscle strength plateaued after four months. These results suggest that VO₂peak should be measured every three months and adjusted to an appropriate exercise program to more effectively maintain and improve physical fitness.